1. Field of the Invention
The present invention relates to a liquid crystal lens, and more particularly to a liquid crystal lens in which a liquid crystal layer is driven using electrodes and an image display device including the same.
2. Discussion of the Related Art
Among the types of devices used to display images is the liquid crystal display (LCD) device. A typical LCD device includes first and second electrodes facing each other and a liquid crystal layer disposed between the first and second electrodes. Liquid crystal molecules of the liquid crystal layer are driven by an electric field generated by applying a voltage between the first and second electrodes. The liquid crystal layer has a polarization characteristic and optical anisotropy. The polarization characteristic may be defined as the tendency of the ends of liquid crystal molecules to become arranged in a single alignment direction, with the alignment direction of the liquid crystal molecule varying in accordance with the electric field when the liquid crystal molecule is disposed in the electric field. In addition, the optical anisotropy may be defined as the emitted light path or light polarization state variation according to the direction of incidence of light on the liquid crystal due to the thin and long shape of the liquid crystal molecule and the alignment direction of the liquid crystal molecules.
Accordingly, the liquid crystal layer shows a variation in the transmittance of incident light with a variation in the voltage applied between the first and second electrodes, allowing an image to be displayed by changing the transmittance of the liquid crystal of a pixel.
A liquid crystal lens has been suggested in which liquid crystal is used as a lens. A typical lens controls the path of light incident on the lens using a difference in properties between a material of the lens and air. When portions of a liquid crystal layer are driven by differing electric fields by applying different voltages across respective portions of the liquid crystal layer, the incident light entering the liquid crystal layer undergoes different phase changes in accordance with the location of the light incidence onto the liquid crystal. As a result, the liquid crystal layer can be used to control the path of incident light in a manner similar to that of a conventional glass lens.
Hereinafter, the structure and operation of liquid crystal lens of the related art will be explained with reference to FIGS. 1A, 1B, and 2.
FIG. 1A is a schematic perspective view of a liquid crystal lens according to the related art, and FIG. 1B is a schematic cross-sectional view of a liquid crystal lens according to the related art.
In FIGS. 1A and 1B, a liquid crystal lens 10 includes first and second substrates 20 and 30, and a liquid crystal layer 40 between the first and second substrates 20 and 30. A first electrode 22 is formed on an entire inner surface of the first substrate 20, and a second electrode 32 is formed on an inner surface of the second substrate 30. A first portion of the second electrode 32 is spaced apart from an adjacent second portion of the second electrode 32 by a predetermined separating distance “d.”
When voltages are applied to the first and second electrodes 22 and 32, an electric field is generated between the first and second electrodes 22 and 32. Because the second electrode is separated into two portions rather than being formed of one continuous shape over an entire surface of the second substrate, the electric field generated between the first and second electrodes 22 and 32 is not uniformly vertical. In other words, while a first portion of the electric field between the first and electrodes 22 and 32 away from the separating portion 32a of the second electrode 32 is substantially vertical, a second portion of the electric field generated in the area adjacent to the separating portion 32a of the second electrode 32 has a direction sloping between the first and second substrates 20 and 30.
Accordingly, the intensity and the direction of the electric field generated by the first and second electrodes 22 and 32 each may vary in accordance with distance away from the separating portion 32a of the second electrode 32. As a result, the light passing through liquid crystal layer 40 driven by the electric field undergoes a change in phase that varies in accordance with the distance of the light from the separating portion 32a of the second electrode 32.
FIG. 2 illustrates the relationship between the phase change of incident light when light passes the liquid crystal lens of FIGS. 1A and 1B and the position of incidence of the light on the liquid crystal lens. FIG. 2 additionally graphically displays the phase change of light through a conventional glass lens for purposes of comparison.
In FIG. 2, first, second and third curves 40a, 40b and 40c show a phase change of light passing the liquid crystal lens, and a fourth curve 40d shows a phase change of light passing the an conventional optic lens made of glass or the like. As may be appreciated by considering the first, second and third curves 40a, 40b and 40c, the shape of the phase change curve for light passing the liquid crystal lens is symmetric shape with respect to the position of the separating portion 32a (of FIGS. 1A and 1B) of the second electrode 32 (of FIGS. 1A and 1B).
The series of first, second and third curves 40a, 40b and 40c correspond to phase change curves for gradually increasing values of the separating distance “d” (of FIGS. 1A and 1B). However, even when the separating distance “d” (of FIGS. 1A and 1B) is appropriately finely controlled, the range of control range of the phase change characteristic of the liquid crystal lens is substantially limited. For example, the range of control does not allow obtaining a phase changing characteristic substantially similar to the phase change curve for a conventional glass lens. For example, while the first and second curves 40a and 40b overall illustrate smaller phase change than the fourth curve 40d, the third curve 40c overall illustrates a larger variation in phase change than the fourth curve 40d for the conventional glass lens.
The shape of the phase change curve is dependent on only the voltage applied to the second electrode 32 and the separating distance “d”. Consequently, even if the phase change of the liquid crystal lens is appropriately controlled by controlling the applied voltage, it is impossible to obtain the same phase change characteristic as obtained using the conventional glass lens.